(1) The network or reticulum formed by the fibrils or granules thinly scattered in the cytoplasm.
(2) The network of granular materials that stain readily with certain dyes within the nucleus, as in nuclear spongioplasm.
(3) The rows of granules in an axon that stain readily with certain dyes.
Spongioplasm is apparent within cells that have been fixed with reagent and stained with dyes when viewed under the microscope. The relative amounts, sizes, and shapes of the meshes of the spongioplasm differ from one cell to another.